The present invention relates to an apparatus for detecting the rotational angle of the crankshaft, or the crank angle, of an internal combustion engine.
The piston in each cylinder of an internal combustion engine is connected to a crankshaft by a connecting rod. Reciprocation of the pistons rotates the crankshaft. The position of each piston in the associated cylinder is detected based on the rotational angle of the crankshaft, or the crank angle. The crank angle is detected by a crank angle detecting apparatus. The detected crank angle is referred to in several engine control procedures that are performed in synchronization with the strokes (intake, compression, expansion and exhaust strokes) of the engine cycle. Specifically, engine control procedures such as ignition timing control and injection timing control are performed based on the crank angle.
Japanese Unexamined Patent Publication No. 5-288112 discloses a crank angle detecting apparatus that includes a rotational speed sensor located in the vicinity of the crankshaft and a cylinder distinguishing sensor located in the vicinity of the camshaft. The rotational speed sensor includes a crank rotor secured to the crankshaft and an electromagnetic pickup facing the crank rotor. The crank rotor has teeth that are angularly spaced apart by thirty degrees and a vacant space that has no tooth and is sixty degrees wide. The rotational speed sensor outputs a pulse, or rotational speed signal, every time each tooth passes by the pickup.
The cylinder distinguishing sensor includes a cam rotor secured to the camshaft and an electromagnetic pickup facing the cam rotor. The cam rotor has a detection tooth. The distinguishing sensor outputs a cylinder distinguishing signal every time the pickup detects the detection tooth. In other words, the distinguishing signal is output every time the cam rotor rotates three hundred sixty degrees, which corresponds to a crank angle of seven hundred twenty degrees.
The rotational speed signal that is output right after the vacant space has passed by the pickup is defined as a reference position signal. The number of rotational speed signals generated after the reference position signal is counted. If the cylinder distinguishing signal is output at the same time the number of the rotational speed signals reaches a predetermined number, the crank angle that corresponds to a certain stroke of each cylinder is determined. In other words, cylinder distinction is executed.
In this manner, cylinder distinction is executed by means of two sensors (the rotational speed sensor and the cylinder distinguishing sensor) for determining specific cylinders to ignite or to inject with fuel. Further, cylinder distinction is executed after the reference position signal is output, that is, only after the vacant space passes by the pickup.
However, if the engine is stopped immediately after the vacant space has passed by the pickup, cylinder distinction will not be executed immediately after restarting the engine. That is, when the engine is restarted, cylinder distinction is not executed until the crankshaft is rotated by nearly three hundred and sixty degrees, or until the vacant space passes by the pickup of the rotational speed sensor. The delay in cylinder distinction hinders engine starting.